Recent Trends in the Synthesis of Benzimidazoles From o‐Phenylenediamine via Nanoparticles and Green Strategies Using Transition Metal Catalysts

Benzimidazole is a heterocyclic moiety of immense importance as it acts as a primary “biolinker” in diverse synthetic routes to obtain bioactive compounds. Substituted benzimidazoles are known to possess a varied range of pharmacological applications, namely, anti‐cancer, anti‐diabetic, anti‐inflammatory, and antiviral like anti‐HIV and anti‐fungal. A number of reviews covering the important aspects of benzimidazoles such as pharmacological activities, SAR studies, and well‐known methods of synthesis have appeared in the literature. However, green synthetic methods particularly using transition metal (TM) catalysts and their nanoparticles, although being more viable and extensively applied by researchers in the present scenario, have not been exclusively and expansively reviewed. Besides this, the vital precursors required for knitting the skeleton of benzimidazole are mainly o‐aryldiamines. The conventional synthesis generally involved the condensation of these diamines with carbonyl/carboxylic acid derivatives either via high temperature heating or via adding strong acids, mostly resulting in poor yields or mixtures. However, recent trends are replacing these conditions by mild and green conditions through TM catalysts. Therefore, the current review emphasizes on the recent trends adopted in the synthesis of benzimidazoles using condensation reaction of o‐phenylenediamines and various aldehydes/ester/amide/alcohols with TM in a catalytic role in nanoform and under environmentally benign green conditions.     

Large amplitude free vibration analysis of thermally post-buckled composite doubly curved panel embedded with SMA fibers

Thermal post-buckled vibration of laminated composite doubly curved panel embedded with shape memory alloy (SMA) fiber is investigated and presented in this article. The geometry matrix and the nonlinear stiffness matrices are derived using Green–Lagrange type nonlinear kinematics in the framework of higher order shear deformation theory. In addition to that, material nonlinearity in shape memory alloy due to thermal load is incorporated by the marching technique. The developed mathematical model is discretized using a nonlinear finite element model and the sets of nonlinear governing equations are obtained using Hamilton’s principle. The equations are solved using the direct iterative method. The effect of nonlinearity both in geometric and material have been studied using the developed model and compared with those published literature. Effect of various geometric parameters such as thickness ratio, amplitude ratio, lamination scheme, support condition, prestrains of SMA, and volume fractions of SMA on the nonlinear free vibration behavior of thermally post-buckled composite flat/curved panel been studied in detail and reported.     

Revisiting surface diffusion in random deposition

An investigation of the effect of surface diffusion in random deposition model is made by analytical methods and reasoning. For any given site, the extent to which a particle can diffuse is decided by the morphology in the immediate neighbourhood of the site. An analytical expression is derived to calculate the probability of a particle at any chosen site to diffuse to a given length, from first principles. This method may become particularly important in cases where obtaining the continuum limit and solving the corresponding differential equation may not be feasible. Numerical simulation of surface diffusion in random deposition model with varying extents of diffusion are performed and their results are interpreted in the light of the analytical calculations. Systems with surface diffusion show an initial random deposition-like growth upto monolayer deposition, then a deviation due to correlation effects and eventual saturation. An explanation for this behaviour is discussed and the point of departure from the linear form is estimated analytically.     

Study of variation in slab thickness of ionospheric F-region during earthquake by wavelet analysis

The present work deals with the anomalies in ionospheric slab thickness of F-region associated with strong seismic activity. In this regard we have considered ionosonde data of Critical frequency of F2 layer (foF2) and Ionospheric Total Electron Content (ITEC) observed for Athens [38°N, 24°E] and Rome [42°N, 13°E] stations. We have considered three cases of earthquake occurring on December 20, 2007, June 08, 2008 and April 06, 2009 and analyzed the ionosonde data of foF2 and ITEC for slab thickness of F-region of the ionosphere in one-hour interval time series record by filtering the geomagnetic disturbances. The result of the study shows that some unusual perturbations were observed in slab thickness of F-region for some days before the main seismic event. It may be due to the generation of seismogenic electric field above the surface of the earth well before the seismic event. This anomalous behavior of perturbations may be used as earthquake precursor.     

A new methodology for crisp equivalent of fuzzy chance constrained programming problem

This paper deals with a chance constrained programming model, where both fuzziness and randomness are present in the objective function and constraints. The concept of fuzzy random variable, mean and variance of fuzzy random variable, minimum of fuzzy numbers are used in the model. The methodology is verified through a numerical example.     

A structural remedy toward bright dipolar fluorophores in aqueous media

The donor–acceptor (D–A) type dipolar fluorophores, an important class of luminescent dyes with two-photon absorption behaviour, generally emit strongly in organic solvents but poorly in aqueous media. To understand and enhance the poor emission behaviour of dipolar dyes in aqueous media, we undertake a rational approach that includes a systematic structure variation of the donor, amino substituent of acedan, an important two-photon dye. We identify several factors that influence the emission behaviour of the dipolar dyes in aqueous media through computational and photophysical studies on new acedan derivatives. As a result, we can make acedan dyes emit bright fluorescence under one- and two-photon excitation in aqueous media by suppressing the liable factors for poor emission: 1,3-allylic strain, rotational freedom, and hydrogen bonding with water. We also validate that these findings can be generally extended to other dipolar fluorophores, as demonstrated for naphthalimide, coumarin and (4-nitro-2,1,3-benzoxadiazol-7-yl)amine (NBD) dyes. The new acedan and naphthalimide dyes thus allow us to obtain much brighter two-photon fluorescent images in cells and tissues than in their conventional forms. As an application of these findings, a thiol probe is synthesized based on a new naphthalimide dye, which shows greatly enhanced fluorescence from the widely used N,N-dimethyl analogue. The results disclosed here provide essential guidelines for the development of efficient dipolar dyes and fluorescence probes for studying biological systems, particularly by two-photon microscopy.     

Chemical potential and internal energy of the noninteracting Fermi gas in fractional-dimensional space

Chemical potential and internal energy of a noninteracting Fermi gas at low temperature are evaluated using the Sommerfeld method in the fractional-dimensional space. When temperature increases, the chemical potential decreases below the Fermi energy for any dimension equal to 2 and above due to the small entropy, while it increases above the Fermi energy for dimensions below 2 as a result of high entropy. The ranges of validity of the truncated series expansions of these quantities are extended from low to intermediate temperature regime as well as from high to relatively low density regime by using the Padé approximant technique.